Effects of soil applied ammonium plus nytrapirin, on growth and metabolism of four rice cultivars

Abstract

A study made in a greenhouse on the effects of soil applied ammonium-N with and without a nitrification inhibitor on dry matter accumulation, nitrogen and free-sugar contents of four rice (Oriza sativa L.) cultivars. The rice cultivars were Pratão precoce, IR-L63, IAC-25 and De Abril. N-NH₄ (150 ppm) was either applied once at seeding or split in three applications (0,23 and 38 days after seeding). Plants had a higher dry weight in the treatments without than in those with the nitrification inhibitor. Application of 150 ppm of N-NH₄ plus a nitrification inhibitors at seeding, drastically reduced plant dry weight. Among cultivars, De Abril, showed the highest resistance to high levels of N-NH₄ in soils, with or without nitrification inhibitor. Decrease in soil pH was higher in the treatments without inhibitor than in the treatments with inhibitor. Nitrification in the former is assumed to be responsible for this lower pH, while in the later, pH drop may be caused mainly by H⁺ -extrusion due to higher cation than anion uptake. Plants without a nitrification inhibitor had higher levels of free amino-N than plants with the inhibitor, the reverse was true for the free sugars levels. There was a negative (- 0,67**) correlation between the root/shoot relationship and dry matter accumulation of plants under the NH₄ plus a nitrification inhibitor treatments. It is suggested that, under proper conditions. NH₄-N and a nitrification inhibitor could be used in upland rice fertilization, with a reduction in N- losses and pH drop.